In a surprise, Munoz appeared on a conference call Thursday with investors and media, saying he is steadily increasing his participation in company activities. His comments gave a boost to United Airlines stock (UAL), which rose 1% to $45.59 at 11:13 a.m., reversing pre-market losses.

"I am certainly darn glad to be here," Munoz said. "I certainly will be back full-time by the end of the first quarter, if not sooner."

Munoz took office in September after a period of chronic delays and computer issues for United, which was ranked as the ninth of 10 North American airlines for on-time performance.

"We are working extremely hard to become the consistently reliable airline our customers can depend on," Brett Hart, acting CEO of United, told investors on Thursday.

Jim Compton, vice chairman and chief revenue officer for United, said the company is also taking actions to bolster its revenue by introducing an "entry-level fare" aimed at "price-sensitive" customers later in 2016.

He said the company would also reduce capacity at its Houston hub, where slumping energy prices are reducing corporate travel. United will shift capacity to "other growing markets like Denver and San Francisco," Compton said.

The company's net income rose from $28 million in the fourth quarter of 2014 to $823 million in the last quarter, while full-year profit rose from $1.1 billion to $7.3 billion. Earnings per share was $2.24 in the fourth quarter, up from $0.07 a quarter ago, and $19.47 for the year, up from $2.93.

S&P Capital IQ consensus estimates pegged the company's fourth-quarter revenue at $9.1 billion and net income at $944 million with earnings per share of $2.49.

Lower oil prices fueled a sharp decline in operating expenses, which fell 8.4% to $8 billion for the quarter, compared to a year earlier.

United Continental doled out $520 million on share buybacks during the quarter.

The company said Thursday that it would acquire 40 new Boeing 737-100 planes in mid-2017, largely for regional partners, in a continuing effort to reduce its reliance on smaller and less profitable 50-seat aircraft.